The present invention relates to methods for making semiconductor devices, in particular, semiconductor devices that include high-k gate dielectric layers.
MOS field-effect transistors with very thin silicon dioxide based gate dielectrics may experience unacceptable gate leakage currents. Forming the gate dielectric from certain high-k dielectric materials, instead of silicon dioxide, can reduce gate leakage. Such a dielectric may not, however, be compatible with polysiliconxe2x80x94the preferred material for making the device""s gate electrode.
When the gate dielectric includes a high-k film, a thin layer of silicon dioxide or silicon oxynitride may be formed between the channel and the high-k film to maintain acceptable electron mobility on the high-k film. When such a buffer layer is added to a very thin gate dielectric, the high-k film must be extremely thin, e.g., less than about 10 angstroms thick. When such an ultra-thin high-k film comprises an oxide, it may manifest oxygen vacancies and excess impurity levels. Oxygen vacancies may permit undesirable interaction between the high-k film and the gate electrode. When the gate electrode comprises polysilicon, such interaction may alter the electrode""s workfunction or cause the device to short through the dielectric.
Accordingly, there is a need for an improved process for making a semiconductor device that includes a high-k gate dielectric. There is a need for such a process for producing a device that is not shorted through the gate dielectric. There is a need for a process for forming a very thin gate dielectric, which includes a buffer layer and a high-k film, that improves the interface between the high-k film and the gate electrode by repairing oxygen vacancies in the high-k film and removing impurities from that film. The method of the present invention provides such a process.